Using Salt as Antifreeze in Black Water Tank

[heintje23]

My black water tank is still half full while the boat is already on the hard. I know, bad planning. I don't really feel like pumping it out with jerry cans.

Is it a solution to just add a couple of pounds of salt and be done with it? And then flush it out really good in the new season.

It is an aluminium tank with grade 80 PVC piping.

[xymotic]

I think I would put in a bunch of -100F antifreeze rather than salt. I don't think salt will do anything to prevent the solids from freezing. (dunno if anything will) but also if you completely saturated it w/salt it would still freeze @ -21.1c Vs -73c for antifreeze, and remember that you'll not be able to saturate the tank w/Salt, and you'll also be diluting antifreeze and raising those temps considerably.

[peghall]

Because urine is so corrosive, any metal black water tank that's more than a couple of years old is living on borrowed time...so leaving the tank full for the winter, even without salt, is not a good plan. Adding salt certainly won't extend the tank life...and depending how cold it can get and how much is in the tank, it may take a LOT more than just a couple of pounds to provide any protection from freezing.

So you really do need empty the tank AND thoroughly flush it out before the boat sits...no easy task, judging from the size of your boat. But if you can get a portable pump and water hose to it, or a barrel to catch discharge from a macerator pump, I urge you to do it.

[avb3]

Salt won't protect your tank from freezing, and is corrosive to it as well.

Pump it out... the only solution.

[heintje23]

Bit the bullit and pumped it out. Thanks for all the advice!!!

[peghall]

Hopefully you also flushed it out thoroughly to remove sludge that will be impossible to remove if it hardens into "concrete."